/Engine/Plugins/FX/Niagara/Source/NiagaraEditor/Public/Widgets/SItemSelector.h
An optional delegate called to get a stable key (supports GetTypeHash()) for an item. If set, this delegate is used to uniquely key items to preserve selection and expansion state when refresh is called.
WidgetArgsType & OnGetKeyForItem &40; const FOnGetKeyForItem & InDelegate &41;